An important approach to disease gene mapping is investigating whether a single nucleotide polymorphism (SNP) is functionally involved in a disease. For complex diseases, the problem is complicated because, unlike Mendelian diseases, their genetic causes might involve many genes and hundreds of alleles. Although there are millions of SNPs deposited in public SNP databases, only a small proportion of them are functional polymorphisms that contribute to disease phenotypes. Thus, prioritizing SNPs based on their phenotypic risks is essential for association studies (1).
